In the field of cardiopulmonary surgery which often involves an extracorporeal blood circulation, there is a demand for blood oxygenators to replace the breathing function of the lungs by removing carbon dioxide from the blood and feeding oxygen to the blood. The extracorporeal blood circulation is required to replace all functions of the patient's heart and blood circulation system, thus fulfilling its special requirements as to blood flow, blood temperature, exchange of carbon dioxide and oxygen. The physiological properties of the blood shall not be altered in the extracorporeal blood circulation system. Various blood oxygenators for use in cardiopulmonary surgery are known.
EP-A-0 089 122 discloses a hollow fiber blood oxygenator having a mat of a plurality of contiguous fiber layers around a porous core, wherein contiguous fiber mat layers exhibit an angle of divergence from the longitudinal axis of the core, wherein the sense of divergence changes in every layer. The blood flows radially across the fiber mat. The fibers do not substantially fill the whole of an annular chamber around the core.
EP-B-0 187 708 discloses a hollow fiber blood oxygenator, wherein fibers or small fiber ribbons are wound helically around a core, wherein a first plurality of fibers is wound in one sense and a second plurality of fibers is wound in the other sense similar to a yarn winding operation. The blood flows axially through the fiber windings, which occupy substantially all of an annular chamber around the core. Gas flow and blood flow may be counter-current.
U.S. Pat. No. 4,239,729 discloses a hollow fiber blood oxygenator, wherein fibers are arranged axially in an elongated housing and do not substantially fill the housing. Blood flows through the fibers whereas the oxygenating gas flows radially with respect to the fibers.
U.S. Pat. No. 3,422,008 discloses a hollow fiber blood oxygenator and a method for forming it, wherein hollow fibers are helically wound on the core in such a way that intermediate helical windings are reversed. Thus, successive layers have opposite winding sense with respect to the, core axis. The blood flow is radial. The annular space is not substantially filled with the fibers.
U.S. Pat. No. 4,031,012 discloses a separatory apparatus which can be used as an oxygenator comprising a card-shaped core on which hollow fibers are wound either parallel to the core, having an angle to the core axis, or having a cries-cross arrangement or zigzag arrangement with respect to successive layers in which the angle is reversed. A counter-current flow of blood and oxygen is preferred, wherein the blood flows outside the hollow fibers.
GB-1 481 064 discloses a membrane apparatus which may be an oxygenator having hollow fiber bundles being contained in a receptacle but not substantially filling it. An angle of 10 to 40.degree. may be formed between adjacent layers of fiber bundles. The fluid flow is principally radial.
U.S. Pat. No. 4,141,835 discloses a dialysis apparatus, wherein a number of separated fibers are arranged in a straight line in a housing. The housing is not filled with the fibers which may also be arranged in helical lines. A fluid flows axially outside the fibers.
EP-A-0 093 677 discloses an apparatus which can be used as an oxygenator in which rolled mats of fibers are arranged, in which the fibers may be crossed in an angle between 1 and 5.degree.. The blood flows in the fibers.
The known hollow fiber oxygenators exhibit a number of disadvantages depending on their construction. They are bulky, have a short blood flow path through the oxygenator and have, thus, a small contact zone for the blood and the gas and consequently a short residence time for the blood in the oxygenator which leads to a poor gas exchange rate. Blood and gas pressure drops may occur as well as channeling of blood or stagnation of blood in certain areas of the contact zone between blood and gas.